Organic contaminants in the pulp and papermaking processes cause serious problems for both paper quality and pulp and paper making efficiency. These contaminants generally include naturally occurring wood pitch or wood resin and synthetic materials such as stickies found in fibers from recovered fiber sources or from mill processes. Wood pitch includes triglycerides, fatty acids, resin acids, steryl esters and sterols. Wood resins, as well as other extractives such as lignans, pectins, and phenols, are the major components of pitch deposits. During the mechanical pulping process and subsequent treatments, the wood pitch is released from the surfaces of fibers and accumulates in the whitewater in the form of colloid particles. The pitch can also contain inorganic compounds such as calcium carbonate, talc, clay, titanium oxide and alum hydroxide or reaction products of resin or fatty acids with metal ions.
Stickies generally refer to the undesirable organic contaminants present in the recycled fibers. Stickies often contain the same natural materials found in pitch deposits as well as synthetic materials including adhesives such as styrene-butadiene copolymer, polyacrylate and polyethylene, hot melts such as ethylene vinyl acetate and polyvinyl acetate, waxes, mineral oils, styrene-acrylate, and wet-strength chemicals such as melamine-formaldehyde. Since stickies are composed mainly of synthetic materials, they are more inclined to deposit on equipment surfaces containing plastic materials such as paper machine wires, wet felts, dryer felts and dryer cans.
Pitch and stickies have a detrimental impact on the pulp and papermaking process, reducing paper machine efficiency and paper quality. Wood pitch and stickies have very low surface energy and tend to deposit on pipe surfaces, chest walls, wires, uhle boxes, doctor blades, fabrics, wet felts, dryer felts, dryer cans and calendar stacks. Deposition of pitch and stickies results in operational difficulties and the malfunctioning of mill equipment. When recycled paper is used, the stickies in the waste paper can accumulate on mill equipment resulting in similar problems. When mechanical pulp is co-present with recycled paper, the combination of wood pitch and stickies generally increases the amount of deposition. Accumulated pitch or stickies particles contaminate the paper sheet when they break free from metal, ceramic, and plastic surfaces of mill equipment causing off quality paper and paper machine breaks. The increased use of recycled fiber can significantly aggravate the problem.
Conventional techniques for pitch and stickies control include dispersion, detackification, adsorption and cationic fixation. Dispersion chemicals include surfactants, polymers, and inorganic dispersants such as polyphosphates. Adsorption materials include talc which interacts with pitch or stickies surfaces to render them less tacky. Talc can be effective for synthetic stickies materials, particularly stickies particles, by adsorbing the particles which aids in dispersing the pitch in the stock and whitewater system and reduces the deposition of pitch on the machine wires and felts.
Various kinds of surfactants and water soluble polymers have been investigated to control the deposition of organic contaminants contained in the fibers of the pulp and papermaking processes.
U.S. Pat. No. 3,992,249 to Farley discloses a chemistry for preventing the deposition of adhesive pitch particles on pulp-making equipment using anionic vinyl polymers containing at least 25-85% of hydropobic-olephilic linkages selected from styrene, isobutylene, methyl styrene, ally stearate, octadecyl acrylate, octadecene, dedecene, n-octadecylarylamide, vinyl stearate and vinyl dodecyl ether and at least 15-75% hydrophilic acid linkages selected from acrylic acid, methacrylic acid, and maleic acid, itaconic acid, acrylamidoacetic acid, maleamic acid and styrenesulfonic acid. The copolymers are anionic in nature.
U.S. Pat. Nos. 4,871,424, 4,886,575, and 4,956,051 describe the use of water soluble polyvinyl alcohols having 50% to 100% hydrolysis to inhibit pitch deposition from pulp in paper-making systems. The polymer is a water-soluble copolymer having recurring entities of nonionic hydrophilic units of vinyl alcohol and hydrophobic units of vinyl acetate. The molecular weight of the polyvinyl alcohol ranges from 90,000 to 150,000. It is preferred that the degree of hydrolysis is in the range of 85% to 90% and that the polymer has a molecular weight around 125,000. Polyvinyl alcohol is often used as an industry standard for comparing different organic contaminant control chemicals.
EP 0568229A1 describes the use of hydrophobically modified hydroxyethyl cellulose (HMHEC) for preventing the deposition of pitch and stickies.
WO2004/113611 and U.S. Pat. No. 7,166,192 to Steeg describe methods for controlling pitch and stickies by adding HMHEC and cationic polymers to a cellulosic fiber slurry.
The prior art describes the use of different surfactants and polymers in the prevention of pitch and stickies. Each of those chemistries has their own limitations, however, and is only effective for a narrow range of organic contaminants.
There exists a need for improved materials and methods for the prevention and/or control of pitch and stickies deposition.
Therefore, it is an object of the invention to provide materials and methods for the control and/or prevention of pitch and stickies deposition.
It is a further object of the invention to provide materials and methods for preventing and/or controlling pitch and stickies deposition wherein the materials and methods are effective for a variety of pitch and stickies components.